Preparation of esters



Patented July 27, 1948 merm'rrom or names mm.- W. Strassburg, Minneapolis, Minm, man or to United States Rubber Company, New York, N. Y., a corporation oi New Jersey No Drawing. Application June 14, 1941.

. Serial No. 754.778

Claims. (01. zoo-4s?) This invention relates to a method for the alcoholysis of alkyl esters of a-hBJOBCllO aliphatic carboxylic acids with Z-propenyl alcohols.

For the alcoholysis of esters, the prior art has employed both acidic and basic catalysts to promote the reaction. However, in alcoholysis reactions involving 2-propenyl alcohols, e. g., allyl alcohol or methallyl alcohol, the use of acidic catalysts is ordinarily precluded in commercial operations by the tendency of such unsaturated alcohols to rearrange into other compounds in the presence of acids thereby decreasing the yield of the resulting 2-propenyl esters to an uneconomical level. Moreover, in the alcoholysis oi esters of u-halogeno acids such as a-ChlOl'O acids, the use 01' the conventional basic catalysts is likewise disadvantageous because of the lability o! the halogen atoms of a-halogeno aliphatic acids and their esters in alkaline media. Other catalysts occasionally employed by the art such as aluminum ethoxide and aluminum powder have likewise proven inefiectual.

I have now found that the alcoholysis of alkyl esters of a-halogeno aliphatic carboxylic acids with 2-propenyl alcohols proceeds rapidly and smoothly in the presence of elemental zinc to give high yields of the desired 2-propenyl esters of a-halogeno aliphatic acids. This catalytic eflect oi. elemental zinc, which I have discovered is highly specific, since other elements of the same group, e. g., cadmium and mercury, display little or no catalytic activity in these alcoholysis reactions; and while a limited number of zinc salts, e. g., zinc chloride, do promote the alcoholysis to a limited extent their efiect is far less than that of elemental zinc itself. The amount of the zinc catalyst operable in my invention may be as little as 0.1% by weight based on the weight of the reactants and need seldom exceed 1.0%. To secure the optimum catalytic efiect, the zinc is preferably employed in a form such that it resents a very highly extended surface, e. g., a finely divided form, such as commercial zinc dust. The amount of the catalyst employed will depend somewhat upon how highly extended it is. The range given above applies to zinc powder which is sufficiently finely divided to pass a IOU-mesh sieve.

The method of my invention is applicable to alcoholysis reactions involving 2-propenyl alcohols of the type formula where R is hydrogen, chlorine or lower alkyl, such as allyl alcohol, methallyl alcohol, ethallyl alco- PATENT OFFICE 2 ho], crotyl alcohol, 2-chloroallyl alcohol and tiglyl alcohol.

Any alkyl ester of the a-halogenated aliphatic carboxylic acid may be employed in the practice of the present invention. The alkyl group may have from 1 to carbon atoms. Thus it may be methyl, .propyl, butyl, hexyl, etc. It is preferred that the alkyl group of the ester employed as starting material be one 0! which the correspondlO ing alcohol is suillciently lower-boiling than the z-propenyl alcohol employed to permit forcing of the alcoholysis reaction to essential completion by distillation of the alcohol formed during the reaction. Thus. for example, the alcoholysis of )5 methyl trichloroacetate with allyl alcohol is carried out by heating the reaction mixture at the boiling point of methyl alcohol, which distills out 01 the reaction mixture as rapidly as it is formed.

My invention has greatest importance when apso plied to alkyl esters of a-Cl'llOl'O aliphatic acids but it is also applicable where a halogen other than chlorine, such as bromine or iodine, is substituted on the carbon atom alpha to the carboxylic group of the acid. Any a-halogenated aliphatic car- 28 boxylic acid may be used in the practice of my invention. Examples are saturated monobasic acids such as acetic, propionic, n-butyric, isobutyric, valeric, and higher homologs ranging: up

, to stearic; saturated dibasic acids such as malonic,

30 succinic. glutaric, adipic, pimelic, suberic, aaelaic,

, sebacic, etc.;.unsaturated monobasic acids such as acrylic, methacrylic, crotonic, vinylacetic, dimethylacrylicf allylacetic, angelic, tiglic, undecylenic, oleie, etc.; unsaturated polybasic acids such as maleic, fumaric, citraconic, mesaconic, itaconic, etc.

Exemplary of the lower-alkyl esters of chalogeno aliphatic acids which may be employed in carrying out the present invention are the methyl and ethyl esters of chloroacetic acid, trichloroacetic acid, a-chloropropionic acid, a,a-dichlorostearic acid and a-chloroacrylic acid.

The relative proportions of thealkyl ester of the a-halogenated alpihatic carboxylic acid and the 2-propenyl alcohol may vary within wide limits. However, it is preferred to use a considerable excess of the Z-propenyl alcohol because it promotes the reaction in the desired direction. Generally at least 1.5 mols of the Z-propenyl alcohol per mol of the alkyl ester or the a-halogenated aliphatic acid will be employed. Preferably from 1.75 to 2.25 mols of the 2-propenyl alcohol per mol of the ester are used.

Since the 2-propenyl esters formed by the method of my invention are polymerizableyit is in more detail; all parts are by weight.

preferable after their preparation to distill them.

e.g., in purification, in the presence of conventional, polymerization inhibitors. For this-"pur ose I have found sym-di-p-naphthyl-p-phen- ,ylenediamine to be particularly satisfactory since it can be added before or during the alcoholysis reaction without detrimental effect. Other suitable polymerization inhibitors include related -1 compounds or the antioxidant type. e.g., phenylp-napthylamine.- sym diphenyl p; ephenylenein: iormed in the reaction dlstills oi! continuously, at atmospheric pressure.

' When distillation oi ethanol ceases, the unreacted methallyl alcoholis removed by distillation at 25 mm. pressure. Distillation oi the residue yields 357 parts (80% of theory) or methallyl chloroacetate.

diamlne, acetone-aniline reaction' products, and the commercial rubber antioxidants known to the art as acetone-dlphenylarnlne condensates. other polymerization inhibitor which'is efl'ective to, prevent polymerization of any unsaturated material present. whether it be-the desired 2- may be employed. The amount of the polymer- Any ' propenyl ester or the reactant 2-propenyl alcohol,

ization inhibltor'may vary widely depending upon the particularone which is employed, the par-.

ticular unsaturated materials present, the temperature, etc., but the amount thereof may-conveniently range from 0.1% to 2% by weight based on the weight of the reactants originally em: ployed. The inhibitor-may be addedat the start of the alcoholysis reaction, during the reaction, or after it has been completed but priorto thedistillationof. the z-propenyl ester product.

- In accordance with a typical method of carry-j- .ing out my invention, a mixture of the alkyl ester of the a-halogenated aliphatic acid, an excess of the '2-propenyl alcohol, and "the elemental zinc catalyst, together with a polymerization inhibitor if desired, is placed in a suitable reaction vessel and heated to the boiling point. 'at which point the saturated aliphatic monohydric alcohol lib- 'rnesh metallic, aluminum. 0.1 part of zinc chloride, the alcoholysis reac-- tion-yleids only 39% of the theoretical amount sp. gr; 211.133

chlorine, 23.8% (theory. 23.9%).

Repetition of the above procedure in the ab-.

sence of zinc yielded none of the methallyl ester.' The same negative results are obtained in the presence of aluminum ethylate and of In the presence oi oi the methallyl ester.

I Example 2 A mixture of- 340 parts of ethyl a-GhlOl'ODi'O- pionate,-360,parts of methallyl alcohol and 1.7

parts oi zinc dust is reacted in the manner oi f Example 1. After the ethyl alcohol has been removed in the same way as in Example 1, 1.7 parts of sym-di-fl-naphthyl p-phenylene-diamine are added, and the reaction mixture is evaporated -at mm. to remove unreacted methallyl alcohol.

The resdue is distilled to yield 353 parts "(78% of theory) of methallyl-a-chloropropioerated by the alcoholysis is vaporized, and the manner to separate; the liberated monohydric alcondensed and collected. The saturated monohydric alcohol withdrawn from the system may be put to any desired use, as for example for es- 21.7% (theory, 21.8%).

, Example 3 l A mixture of 366 parts of ethyl chloroacetate, 360 parts of allyl alcohol, 1.8 parts of zincdust and- 1.8 parts oi. syin-di-fl-naphthyl p-phenyla enediamine is charged into the distillation appa-.. ratus described in Example 1. The reaction mixture is heated to such temperature that ethyl;

alco'holdistills ofias it is formed, at atmospheric pressure. At the end of the reactionthe unreacted allyl alcohol is removed by evaporation at approximately mm. and the residue issubmitted to vacuum distillation. In, this way are obtained terifyinga-halogenated aliphatic acid to form more ester for feeding to the reaction zone. After the reaction is completed, as, indicated by the-cessation .ot distillation oi the saturated monohydricalcohol, the residual reaction mixture may be distilled, preferably under reduced pressure in order to minimize decomposition -reactions, to'recover first a fraction of the unr e acted excess a-propenyl alcohol and then a fraction of the 2-propenyl ester of the a-halogenated carboxylic acid.

' The processdescribed aboveis illustrative of 366parts (91% of theory) of allyl chloroacetate, B. 68-69 C./20 mm; .n "=l.4455; chlorine, 26.2% (theory, 26.3%). 1

- Example 4:

' A mixture of 883 parts oi ethyltrlchloroacetate, 280 parts of methallyl alcohol, 1.7 parts of zinc dust and 1.7 parts of sym-di fi-naphthyl-p-phenylenediamine is charged into a distillation vessel similar to that of Example 1. The reaction is carthe batchwise methods which are most suitable for laboratory and small scale operations. Howv ever the process can be modified in an obvious manner to permit continuous operation which is preferable for large scale production.

The following examples disclose my invention Example 1 A mixture'of 366 parts ofethyl chloroacetate, 432 parts of methallyl alcohol, 2 partsof zinc dust and 2 parts of sym-di-p-naphthyl-p-phenylenediamine are charged into a distillation vessel fitted with apacked c'olu'mn arid variabletakeoft distillation head. The reaction mixture is heated to such temperature that the ethanol-beried out as in previous examples and ethyl alcohol is distilled continuously frornthe reaction 1 mixture ash is formed, together with a small amount of isobutyraldehyde formed as an incl.-

dental by-product. The alcoholysis reaction. l

yields 188 parts of methallyl trichloroacetate,

- B. Ii-76 C./ 10 mm.; n ?1.-i672; chlorine, 48.08% (theory, 48.8%).

Example. 5

dust and 0.14 part 0i sym-di-p-naphthyi-pphenylenediamine is heated Ior approximately four hours at a temperature suflicient to efiect distillation of the methanol formed during the reaction. At the end of the reaction, the'unreacted allyl alcohol is, evaporated under diminished pressure-as in previous examples, and the residue is distilled in vacuo yielding 17.9 parts of allyl a-chloroa'crylate, B. 69-70 C./24 mm. n 1.4585.

A mixture of 30.1 parts of methyl a-chloroacry-" late, 29 parts of allyl alcohol, 0.14 part of zinc Having thus described my invention. what I claim and desire toprotect by Letters Patent is:

l. A method of preparing Z-propenyl esters of a-halogenated' aliphatic carboxylic acids which comprises heating a mixture of a lower alkyl ester of an w-halogenated aliphatic carboxylic acid and a 2-propenyl alcohol, the saturated aliphatic alcohol corresponding to the lower alkyl group in said ester being substantially lower-boiling than the Z-propenyl alcohol, in the presence of elemental zinc as a catalyst, and distilling the saturated aliphatic alcohol corresponding to the lower alkyl group in said ester out of the reaction mixture as rapidly as it is formed. a

2. A method of preparing 2-propenyl esters of ran-halogenated aliphatic carboxylic acids which comprises heating a mixture oi a, lower alkyl ester of an a-halogenated aliphatic acid and an excess of 2-propenyl alcohol, the saturated aliphatic alcohol corresponding to the lower alkyl group in said ester being substantially lower-boiling than said Z-propenyl alcohol, in the presence of elemental zinc as a catalyst, distilling the saturated aliphatic alcohol corresponding to the lower alkyl group in said ester out oi the reaction mixture as rapidly as it is formed. iractlonally distilling the liberated vapors comprising said saturated aliphatic alcohol, removing an overhead fraction consisting essentially of said saturated aliphatic alcohol, returning the fraction of heavier material to the reaction zone, and, when distillation of said fraction of saturated aliphatic alcohol ceases; distilling out of the reaction mixture the excess of 2-propenyl alcohol under reduced pressure, and thereafter distilling the 2-propenyl ester of said zit-halogenated aliphatic carboxylic acid out of the residual reaction mixture under reduced pressure.

3. The method of claim 1 wherein said a-halogenated aliphatic carboxylic acid is an a-chlorinated aliphatic carboxylic acid.

4. The method of claim 1 wherein the reaction and distillation are conducted in the presence of a polymerization inhibitor efiective to prevent rial present.

ROGER W. STRASSBURB. 

